Air Spark Gap Research Articles

A Realistic Spark-Gap Model in Computer Simulation of Blumlein Transmission Line

Over the years, the use of numerical simulations in the development of high voltage pulse generators has become a standard approach. Nevertheless, the modeling of spark-gaps, one of the most commonly used switching devices in such generators, has always been a weak point of the process, especially in coupled circuit and field simulations. Although the complex SPICE spark-gap models do exist, it is difficult or impossible to directly couple them with field simulations. Thus, in many cases, the spark-gap models used were elementary and required many assumptions, which led to the prolongation of the design process. Our paper describes the coupling of a realistic circuit model of an air spark-gap, with a Finite Element Method simulation, solving the wave equation in the time domain. The simulation describes the operation of a Blumlein transmission line as a pulse generator. One of the advantages of the proposed solution is that the input parameters of the empirical model are measurable physical quantities characterizing the spark-gap circuit. We have carried out two numerical experiments testing the simulation for both the matched, resistive load and for a dipole antenna connected to the output of the Blumlein transmission line. The test results confirm that the circuit-field simulation can model Blumlein transmission lines with both simple elements (e.g., resistors) and complex circuits (e.g., an equivalent circuit of a dipole antenna) attached to its terminals.

Palm top plasma focus device as a portable pulsed neutron source

Development of a palm top plasma focus device generating (5.2 ± 0.8) × 10(4) neutrons∕pulse into 4π steradians with a pulse width of 15 ± 3 ns is reported for the first time. The weight of the system is less than 1.5 kg. The system comprises a compact capacitor bank, a triggered open air spark gap switch, and a sealed type miniature plasma focus tube. The setup is around 14 cm in diameter and 12.5 cm in length. The energy driver for the unit is a capacitor bank of four cylindrical commercially available electrolytic capacitors. Each capacitor is of 2 μF capacity, 4.5 cm in diameter, and 9.8 cm in length. The cost of each capacitor is less than US$ 10. The internal diameter and the effective length of the plasma focus unit are 2.9 cm and 5 cm, respectively. A DC to DC converter power supply powered by two rechargeable batteries charges the capacitor bank to the desired voltage and also provides a trigger pulse of -15 kV to the spark gap. The maximum energy of operation of the device is 100 J (8 μF, 5 kV, 59 kA) with deuterium gas filling pressure of 3 mbar. The neutrons have also been produced at energy as low as 36 J (3 kV) of operation. The neutron diagnostics are carried out with a bank of (3)He detectors and with a plastic scintillator detector. The device is portable, reusable, and can be operated for multiple shots with a single gas filling.

Performance and Structure of an EMP Simulator

The electromagnetic pulse simulator designed in this paper consists of an adjustable direct current high voltage source, a capacitor for energy-storage, an air spark gap switch, a resistive divider for measurement and a GHz transversal electromagnetic wave (GTEM) cell. The analysis model is constructed based on the theory of transmission line. Influencing factors, such as self-load and impedance mismatch of the transmission line (as well as the cell), were analyzed using Pspice. The self-load has the effect of parallel connection with the load of GTEM cell. It may increase the rise-time, decrease the fall time and reduce the voltage peak. The sudden change of the transmission line impedance will make the waveform of pulse contain reflected oscillation. Four types of resistance divider link were also simulated using Pspice. Improper connection of the resistance divider will cause the waveform of pulse oscillation and lengthen the rise-time, which can be reduced by shorting the high voltage lead, using system structure with gradually changing resistance or connecting a damping resistance at the end.

Breakdown characteristics of air spark-gaps stressed by standard and short-tail lightning impulses: Experimental results and comparison with time to sparkover models

The paper reports the results of an investigation carried out in order to determine the critical flashover voltage, and the relevant standard deviation, of the rod–rod air gaps spacing 0.1 and 0.2 m stressed by standard lightning impulse (LI) (1.2/50 μs) and an impulse voltage with short tail (1.2/4 μs). The volt–time characteristics of these spark-gaps under both impulses are also determined and the experimental test results are discussed.Models based on the disruptive effect, as proposed by Kind and by Chowdhuri, are considered and applied in order to reproduce the volt–time characteristics under 1.2/50 and 1.2/4 μs impulses. The viability of the application of these models to the above-mentioned insulation is discussed. The results of the application of the two models are compared with each other and with the experimental characteristics.

Effective laser field influence on the transverse triggering of a spark gap in air

Nd : YAG laser triggering of a centimetric air gap in a homogeneous electric field is studied for pressures ranged from 0.5 to 5 bar. Breakdown transient voltage and current are measured and the formative time lag dependence on reduced field and laser intensity is analysed. It is quantitatively shown that the laser field strongly influences the time lag to breakdown through the effective reduced field.

Femtosecond laser triggering of a sub-100 picosecond jitter high-voltage spark gap

We have demonstrated sub-100 ps jitter operation of a pressurized high-voltage air spark gap triggered by a femtosecond Ti:Sapphire laser. Time delay statistical fluctuations with a standard deviation as low as +−σ=0.037 ns were obtained.

Optimization of a vacuum spark discharge for soft-X-ray emission

A 1-kJ vacuum-spark device has been developed as a pulsed X-ray source for applications in the field of microlithography, microscopy, flash radiography, etc. The optimization works for the pulsed soft-X-ray emission are presented. The optimization was made in two steps: 1) X-ray emission maximization and 2) X-ray emission reproducibility. For the X-ray emission maximization, the changed parameters were the main capacitor energy, the anode-cathode geometry, the anode material, and the trigger pulse amplitude. The best combination is 1 kJ for the main capacitor energy, a conical shape for the anode, 6-12 mm anode-cathode separation, iron for the anode material, and 14-15 kV for the trigger pulse amplitude. In these conditions, energies of up to 10 J per pulse are obtained in the 3-40 keV range for the X-ray pulses. In order to have a good reproducibility, a high-power, very fast, high-voltage trigger pulse is required. To fulfill these conditions, a pulse transformer and an air spark gap were added to the initial triggering device (a magnetic pulse compression circuit). With the new trigger pulse (20 J per pulse, 50-ns rise-time, 22-kV amplitude in an open circuit), an acceptable X-ray emission reproducibility was obtained.

An air breakdown kinetic model

A kinetic model is developed for the glow phase of a spark gap in air. The model includes heavy-particle collisions leading to thermal ionization and electron-collision processes. Rates for the latter are calculated by a computer program that solves the electron Boltzmann equation, verified using empirical measurements. These rates include attachment and ionization, excitation followed by ionization of the excited species, and dissociation followed by ionization of the atomic species; molecular-impact detachment was found to be necessary to match experimental closing times. With those processes, the model predicts closing times well, over a wide range of voltages above and below the dc breakdown voltage.

A simple monochromatic spark discharge light source

A compact spark discharge tube operated as a monochromatic light source at 587.5 nm is described. The device is powered by a small 25-kV, 3300-pF doorknob-type capacitor switched by an atmospheric air spark gap. The peak luminous intensity of the 587.5-nm line emission from the helium spark discharge operated at 23 kV and 900 mbar is estimated to be 2.1×103 Candela into 4π radians.

An investigation of processes in a laser air spark gap

An investigation of processes in a laser air spark gap

Molecular absorption of pulsed CO2 laser radiation in the presence of a buffer gas

A pulsed CO2 laser with a nonselective resonator (RI8) was used for the experiments, driven by an air spark gap at atmospheric pressure, with a pulse energy stability of • and a modified pulsed CO2 laser with a nitrogen spark gap at higher pressure with a pulse energy stability of • The amount of energy absorbed by the gas in the cuvette (diameter 3.4 cm, length i0 cm) was determined by measuring the transmitted energy (typically 50-95% of that incident) with a KIM-I calorimeter.

Breakdown Characteristics of a Sphere-Plate Triggered Air Spark-Gap

Experiments have been designed and performed on a sphere-plate triggered air spark-gap with the purpose of separating the factors affecting dc breakdown process, and investigating the physical aspect of the phenomenon. Measurements of minimum break- down voltages and corresponding time-lags have been carried out with all the influencing factors of triggering spark present, as well as with each factor acting alone. The results of the experimental analysis have lead to certain conclusions regarding the influence of each affecting factor, of the polarities of main and triggering gaps, and of triggering voltage on breakdown characteristics and on gap behaviour more generally.

Spark Gap Power Switching for Conical θ-Pinch Plasma Gun

A simple, easily maintained air spark gap of ∼7 nH inductance was developed to switch 0.24 C stored charge at 20 kV in an LC circuit having a period of ∼4 μsec. A similar 3 nH spark gap with an auxiliary triggering circuit was used to clamp the magnetic flux within the load near the voltage minimum. Voltages up to 30 kV and currents to 5×105 A have been handled. Acoustic noise was minimized by completely enclosing the arc, and forced air venting removed corrosive gases and helped control the temperature to improve reproducibility.

A simple switching system for repeatable pulsed discharges

A switching system has been designed to operate with an overall jitter of 0·2 μs in current breakdown for a 5·7 kJ pulsed discharge. Reproducibility can be sustained for up to 70 consecutive firings. Consisting of two inexpensive open air spark gaps built from readily available materials, the system functions reliably with a minimum of maintenance.

Breakdown of a Spark Gap in Air Triggered by a Laser

Breakdown of a Spark Gap in Air Triggered by a Laser

Long-time-lag discharge in a triggered spark gap in air

Trigatron spark-gap discharges with very long time lags to breakdown were observed and their characteristics investigated in order to determine the discharge mechanism. The main voltage was applied with a predetermined delay after the trigger pulse, and breakdown with a time lag of many hundreds of microseconds at voltages from 30 to 80% of the untriggered breakdown voltage has been observed. Photographs show a distinctive discharge path along a spherical shell around the trigger spark region. These results support the idea that the triggering of these long-time-lag discharges is due to a mechanism evolving in a different way from those previously accounted for triggered sparks.

Breakdown in Triggered Spark Gaps in Air

Trigatron breakdown characteristics were studied in atmospheric air for gaps up to 15 cm in length. Under negative impulse voltages with a positive trigger pulse applied in the grounded electrode, the minimum breakdown values corresponded closely to the negative sphere-rod gap breakdown values. While under positive impulses the trigatron broke down at approximately the same voltages as the positive sphere-rod gaps. The low breakdown in trigatrons under negative impulse voltages was preceded by a positive leader identical to that observed in positive sphere-rod gaps. The higher breakdowns under the positive voltages resulted from a negative leader. The results suggest that the space charge from the auxiliary spark distorts the initially uniform field in the gap and the breakdown follows the nonuniform field breakdown mechanism.

Fast-pulse breakdown of nonuniform-field pressurised-air spark gaps

Pulse-breakdown data in the nanosecond range are given for 3–5 mm nonuniform-field air spark gaps at a pressure of 1–6atm. The 3-electrode gap has a central disc trigger electrode having an edge radius of 0.5 mm. A negative voltage pulse, whose rate of rise increases linearly from 10 to 100kV/ns, is applied to the trigger electrode with various voltages previously applied to the outer main electrodes. Breakdown is initiated with a very low jitter by field emission from the trigger electrode. Comparison with similar data for pressurised uniform-field gaps is made.

Sparkover in Long Uniform-field Gaps

THE object of the work described in this communication was to measure the static breakdown voltages of long uniform-field spark gaps in atmospheric air, and to investigate the mechanism of sparkover. The measurements were made using electrodes of the Bruce profile1, for which sparkover occurred in a uniform electric field at electrode spacings up to 17 cm.

Hard X-rays from Exploding Wires

DURING the past year correlated electrical and X-ray measurements of exploding wires in vacuum have been performed at this laboratory. The wire was axially suspended between the electrodes of a vacuum tube which was coaxially arranged on the energy storage capacitor (ASEA type CTU1, 100 kV, 0.1 µF). A triggered air spark gap, fitted between the vacuum tube and the capacitor, initiated the discharge. The loop inductance, calculated from the frequency of the energy oscillations, was about 150 nH. The tube was continuously evacuated by an oil diffusion pump. The tube pressure was maintained at 1.5 × 10−6 mm of mercury.